Objective Recent studies reveal important roles ofplatelet P-selectin on progression of atherosclerosis.In the present study, we examine the relation between platelet P-selectin expression and severity of acute coronary syndromes.Methods One hundred and eighty-four consecutive patients with proven or clinically suspected acute coronary syndromes (ACS) were enrolled in the study. Level of P-selectin expression was determined by flow cytometry.Platelet P-selectin level was expressed as the percentage of P- selectin positive platelet.Results The level of P-selectin was higher in patients with a single diseased coronary artery or multiple diseased arteries compared to those with normal coronary arteries.P-selectin expression was significantly and positively correlated with angiographic Gensini score (r=0.323,P=0.029).Multiple regression analyses showed that the association of the percentage of P- selectin-positive platelets with ACS was independent of other clinical factors.Conclusions Platelet P-selectin is associated with severity of acute coronary syndromes in patients with acute coronary syndromes. Objective Recent studies reveal important roles of platelet P-selectin on progression of atherosclerosis. In the present study, we examine the relation between platelet P-selectin expression and severity of acute coronary syndromes. Methods One hundred and eighty-four consecutive patients with proven or clinically Level of P-selectin expression was determined by flow cytometry. Platelet P-selectin level was expressed as the percentage of P-selectin positive platelet. Results of the level of P-selectin was higher in patients with a single diseased coronary artery or multiple diseased arteries compared to those with normal coronary arteries. P-selectin expression was significantly and positively correlated with angiographic Gensini score (r = 0.323, P = 0.029). Multiple regression analyzes showed that the association of the percentage of P-selectin-positive platelets with ACS was independent of other clinical factors. Conclusions Pla telet P-selectin is associated with severity of acute coronary syndromes in patients with acute coronary syndromes.